Solar Battery Sizes Compared: What 5kWh, 10kWh and 13kWh+ Actually Means for a South West Home
NIXON
Published 22 October 2026
The right battery size for most South West homes depends on the amount of power you use between sunset and sunrise. For many households, that lands somewhere between 8 and 13 kWh of usable capacity. Smaller homes with low evening use can do well with around 5 kWh, while homes with ducted air conditioning, a pool or an electric vehicle often need more.
The table below is a starting point. Your own bill, your existing solar system and whether you want blackout backup will decide where you land.
Battery Size by Household Type
| Household | Typical evening and overnight use | Starting battery range (usable kWh) |
| 1–2 people, out during the day, gas cooking or hot water | Lights, TV, fridge, some cooking | 5–8 kWh |
| Family of 3–4, electric cooking, split system in the evening | Cooking, laundry, entertainment, one or two split systems | 10–13 kWh |
| Larger home with ducted air, pool pump or EV charging at night | Heavy summer cooling and other large loads after dark | 13 kWh and up, often split across modules |
| Main goal is blackout protection | Depends on which circuits you want to keep running | Sized to your backed-up loads, not your whole bill |
These ranges are general guidance. Your recommended size should come from your own usage data.
What the Numbers Mean
A kilowatt-hour (kWh) is a unit of stored energy. A 10 kWh battery could, in theory, supply 1 kW of load for 10 hours, or 2 kW for five hours. Two main things change how far that goes.
The first is usable capacity. Battery specs often list a total capacity, but what you can actually draw on is a little less. Always compare batteries on usable capacity. The WA Residential Battery Scheme rebate is also calculated on usable capacity, so it's the figure that matters on your quote too.
The second is power output, measured in kilowatts (kW). Capacity tells you how long a battery can run your home. Power output tells you how much it can run at once. A large battery with a modest inverter might still struggle to run a ducted air conditioner, oven and kettle at the same time, and the grid will cover the difference.
What Can a 10 kWh Battery Actually Run?
As a rough guide, a 10 kWh battery could cover an evening of the following in a typical home:
- A fridge for the whole night (around 1 kWh)
- LED lighting, TV and phone charging for the evening (around 1–2 kWh)
- Cooking dinner on an electric cooktop or oven (around 1.5–2.5 kWh)
- A split system cooling a living area for three to four hours (around 3–4 kWh)
- A dishwasher cycle (around 1 kWh)
These figures are approximate, and the actual draw depends on the appliance, its age and how you use it.
A Simple Sizing Guide
1. Look at your bill
Your power bill shows your average daily usage in units (kWh). If you already have solar, it also shows how much you export to the grid.
If you don't have solar yet, the figure that matters is how much of your daily total you use after about 5pm. That varies a lot between households, which is why real usage data gives a better answer than a guess.
If you do have solar, your imported power is a good guide to what a battery could cover, because most of it is drawn at night when your panels aren't producing. If your average import is 9 kWh a day, a battery much bigger than 10 kWh will sit partly empty most nights.
2. Check whether your solar can fill it
If you export 15 kWh on an average day, there's plenty to charge a 10 kWh battery. But if you only export 4 kWh, a large battery won't fill except on the best summer days.
Many older South West systems are 3 to 5 kW, which may not leave much surplus once daytime use is covered, especially in winter. NIXON typically recommends 5–7 kW of solar for a standard home as a starting point, and a household adding a battery to a small older system may need to upgrade panels or the inverter at the same time.
3. Decide whether blackout backup matters
Not every battery keeps the power on in an outage. Backup needs to be designed into the installation. NIXON offers two battery setups for this:
- Essential circuit backup keeps selected circuits running, such as the fridge, lights and Wi-Fi.
- Full home backup covers the whole house and needs a battery and inverter sized to handle all your loads at once.
If you're on a rural property outside Busselton or Margaret River where outages last longer, or you rely on a bore pump or medical equipment, backup may matter more than bill savings when choosing a size.
4. Factor in available rebates
Rebates affect which size makes sense. For most South West homes, the rebates are most generous for batteries up to about 14 kWh. Check the current rebate figures before you commit, since the schemes can change.
Signs a Battery is the Wrong Size
An oversized battery rarely fills and seldom empties, meaning you've paid for capacity you don't use.
An undersized battery runs flat early in the evening most nights, and you're back to buying grid power for the rest of the night. This is easier to fix if the battery is modular and can be expanded later, so ask whether that's an option.
Your usage will also change. If you're planning an EV, a pool, a switch from gas to electric cooking or hot water, or a new ducted system in the next few years, factor that in now.
Getting a Recommendation For Your Home
NIXON's free solar and battery assessments are built around your actual usage and budget rather than a fixed package. We'll check your roof, switchboard and inverter, and show you how the WA and federal rebates apply to the size we recommend.
Contact NIXON Bunbury or NIXON Busselton to book an assessment.
- NIXON Bunbury — 11 Dodson Rd, Glen Iris WA 6230 — (08) 6288 7152
- NIXON Busselton — 102 Strelly Street, Busselton WA 6280 — (08) 6288 7154
